Tropical Oceanic Low-level Cloud Fraction Feedback and its Relation to High-level MSE Advection.
Abstract
The spread of equilibrium climate sensitivity (ECS) between global climate models (GCMs) has been attributed to uncertainties in simulated low clouds radiative feedbacks. Studies have linked this uncertainty to differences in physical parameterizations and free parameters in GCMs. Here, cloud feedbacks are analyzed based on differences in simulated climate from instantaneous quadrupling of CO2 and preindustrial conditions in nine GCMs. Among these GCMs the largest disagreement in cloud radiative feedback (CRF) change is over the tropical eastern Pacific which can be attributed to changes in CRF from low clouds. In terms of total cloud fraction (CF) change the largest disagreement between GCMs is over the central and western tropical Pacific which is due to changes in both high and low clouds. It is found that over the tropical Pacific, change in low-altitude CF is strongly anti-correlated with change in high-altitude CF, which in turn is strongly correlated with change in the upper troposphere moist static energy (MSE) advection. This relationship is generally stronger in GCMs with higher ECS. Within one of the GCMs, CanESM2, the sensitivity of our results to modification of adjustable parameters is explored. Among the group of parameters that were adjusted the greatest sensitivity was found for changes to initial cloud base mass flux of shallow convective clouds with increased values leading to decreased upper troposphere MSE advection and consequently less high-altitude clouds and more low-altitude clouds.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.A43B0219M
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSESDE: 3307 Boundary layer processes;
- ATMOSPHERIC PROCESSESDE: 3310 Clouds and cloud feedbacks;
- ATMOSPHERIC PROCESSESDE: 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES